Variations in Temperature and Rainfall Extremes during the Recent Past: Three Case Studies from Semi-arid Maharashtra, India

Amit G. Dhorde1, Gauri Joshi1 and Anargha A. Dhorde2

1 Department of Geography, University of Pune, Pune – 411 007, amitdhorde@unipune.ernet.in
2 Department of Geography, Nowrosjee Wadia College, Pune 411 001, anargha@yahoo.com

“Society’s perception of climate variability and climate change is largely formed by the frequency and the severity of extremes” (IPCC, 2007). Changes in extremes like intense rainfall, floods, heat and cold waves, etc. have impacts on human activities such as agriculture, human health, transportation, urban development and planning and water resource management. One of the major assumptions of the climate change is that the climate of the future will be dominated by increased extremities in weather. To come to such a conclusion we need to assess the present situation. It only after careful investigation that we can formulate future strategies to combat such changes that may be expected to occur and have negative impact on society. Present study attempts to understand trends in extremes of temperature and rainfall at three locations in semi-arid Maharashtra – Aurangabad, Pune and Solapur. Daily temperature and rainfall data for the period 1969-2006 were obtained from India Meteorological Department (IMD). Based on the percentile values, various temperature and precipitation indices were derived from the data. Heat and cold wave analyses were also carried out. Indices derived from percentiles were further studied for trends using regression analysis. This exercise was performed for different seasons i.e. summer, monsoon, post-monsoon and winter. The results revealed that, during summer, there is no significant change in warm days and nights at all the three stations, but the frequency of very cool nights has decreased significantly at Aurangabad. During monsoon very cool days have significantly increased at Pune with a rate of 2 days/decade. This may be the reason for significant decrease in mean monsoon maximum temperature at this location. Solapur, in post-monsoon season, has recorded significant decrease in very cool days, possible reason for an insignificant rise in mean post-monsoon maximum temperature. When we compared these results with that of heat and cold wave analysis some interesting aspects of the study were revealed. For example, days with heat wave conditions have increased at Aurangabad during summer, but the frequency of warm and moderate warm days does not show any significant increase, in fact the frequency has decreased. This station falls in the category where normal summer maximum temperature is below 40 oC. However, the threshold values obtained from percentiles for warm days are 42.1 to 42.6 oC and for moderate warm days are 41.6 to 42.1 oC. This suggests that, though on one hand heat waves have increased the days with temperature more than 40 oC have decreased. Fascinating results, such as this are obtained for other locations also. The rainfall extremes reveal that wet days of all categories, except one, record insignificant increase at Aurangabad and Pune. Thus, as far as temperature extremes are concerned, warming signals are noticed in some cases, but are not strong enough to make a confident statement.

References:
IPCC (2007) Climate change 2007: The physical science basis, summary for policy makers, contribution of working group I to the fourth assessment report of the Intergovernmental Panel on Climate Change, IPCC Secretariat, Geneva, Switzerland.